The Zebra Mussel (Dreissena polymorpha) is a small triangular mussel with brown and cream-colored stripes on its outer surface. It was introduced into the Great Lakes from Europe in the 1980s and is spreading throughout the Mississippi River drainage. It has no commercial value, but is important because it poses a threat to native mussels by colonizing their shells and competing for food and oxygen. (Conservation Status: Currently Stable)